1. Field of the Invention
The present invention relates to a method for selecting a source transmit antenna in a cooperative multiple-input and multiple-output (MIMO) communication system. More particularly, the present invention relates to a method for selecting a source transmit antenna in a cooperative MIMO communication system for transmitting a signal from a source node to a destination node through a relay node and a computer-readable medium for recording the method thereon.
2. Description of Related Art
In recent years, much research on cooperative communication systems has been conducted to improve the spectral efficiency and reliability of communication systems. The spectral efficiency and reliability of a communication system may be significantly improved by applying multiple-input and multiple-output (MIMO) technology to the cooperative communication system. MIMO refers to an antenna system which enables multiple inputs and multiple outputs. Specifically, MIMO technology allows a base station and a mobile terminal to have two or more antennas to transmit data in multiple paths and allows a receiver to detect signals received in multiple paths, thereby reducing interference and lowering transmission rates.
A conventional wireless communication network, such as a wireless LAN, uses only one of two antennas according to the direction of an access point (AP) configured to connect a wired network with a wireless network. However, MIMO enables two antennas to be operated at the same time for high-rate data exchange. MIMO allows N transmit antennas to transmit independent signals with the same frequency at the same time. As the signals experience different spatial fading on wireless channels, the signals received by receive antennas are not correlated with one another. In this case, since the transmit antennas transmit different signals, data as much as the number of the transmit antennas may be transmitted, thereby transmitting more data than a conventional communication network. For reference, fading is deviation of the attenuation that a carrier-modulated telecommunication signal experiences over certain propagation media.
On the other hand, a multi-antenna source node may obtain a large diversity with a space-time code. However, the use of space-time code needs highly priced RF chains as many as the number of multiple antennas. The RF chain is known to be costly in terms of size, power consumption and hardware. In order to reduce the costs, a conventional point-to-point MIMO system employs a transmit antenna selection technique which is lower in terms of cost and complexity.
Unlike the point-to-point MIMO system, the cooperative communication system has two independent paths, i.e., source-destination node path and source-relay-destination node path. In order to select an improved transmit antenna at a source node, both the source-destination node path and the source-relay-destination node path have to be considered simultaneously. Unlike amplify-and-forward (A&F) relaying technique, however, decode-and-forward (D&F) relaying technique is difficult to derive an accurate signal-to-noise (SNR), making it difficult to find a transmit antenna selection technique.